U.S. Pat. No. 4,398,167 (Dickie et al) entitled "Limited Angle
Electric Rotary Actuator", relates to an electric rotary actuator for producing rotation through a limited angle. The rotor of this actuator is in the form of a cylindrical shell and includes several loop coils arranged in a cylindrical framework. The rotor lies in an annular flux gap defined by a stator magnet assembly and a flux return casing. Each pair of axially extending limbs of the adjacent loop coils lies opposite to and cooperates with a respective stator pole face.
The rotor for this actuator is made by pre-forming the coils and bonding them together at their edges with epoxy resin. The upper horizontal (non-active) limbs of this cylindrical coil structure are then bonded to the outer rim of a partial former. The former consists of an end cap, to which the coils are bonded, and a number of broad finger-like tabs, depending from the cap. These tabs locate exactly in the central apertures of the loop coils to provide additional support. However, they also increase the weight and moment of inertia of the rotor.
An alternative method of manufacture comprising injection moulding the former around the coil structure to encapsulate it is also briefly suggested. However, this has subsequently proved difficult to achieve in practice because of the somewhat complex shape of the partial former and also because of the difficulty of preventing damage to or disturbance of the termination wires of each coil under mould pressures and temperatures.
In U.S. Pat. No. 4,107,587 (Ban et al), entitled "Three phase DC motor having non-superimposed armature coils", there is shown one embodiment (FIGS. 9a and 9b) of such a motor having a rotor of somewhat similar structure to that of European application 31876-Al. Again several loop coils of rectangular plan but arcuate profile are arranged in a cylindrical manner as part of a cup-shaped armature or rotor.
However one difference between this rotor and that of U.S. Pat. No. 4,398,167 is that the coils are spaced slightly apart. A further major difference lies in the support structure for the coils, which are said to be "moulded with plastic into an armature". No details of the moulding process are given but the plastics material extends around the coil peripheries and also forms a disk shaped end cap for the armature. The plastics material also fills the central apertures of the loop coils thereby increasing the armature inertia. The electrical termination of the loop coils of U.S. Pat. No. 4,107,587 is inconvenient in that one end is at the periphery of the coil and the other is within the central aperture. It is not clear how these coil ends would be protected from disturbance and damage if pressure moulding were employed.
Reference is also made to Japanese published patent application 57-75542(A) for "Coil assembly of rotary machine and manufacture thereof". In this application a plurality of flat rectangular coils with rectangular holes at the center and arc sections are arranged cylindrically avoiding their overlapping each other. To arrange the coils cylindrically, an auxiliary member is provided with struts around a ring and the rectangular holes are engaged with convex projections on the struts. The auxiliary member and the coils are next arranged in a metal mold filled with resin to produce a unified coil assembly. No mention appears to be made of the termination of the coils and the protection of the termination during the moulding process.
Reference is also made to Japanese published patent application 55-166448(A) for "Stator for flat type brushless motor". This shows the manufacture of a discoidal rotor by moulding a number of coplanar flat coils into a disk of resin. A moulded terminal lead-out portion is provided on the bottom of each coil, the actual wires being picked out through lead-out holes in the bottom of the mould.